Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$113.94	12.488%	$128.1688	$128.17	$128.15	$128.20
Purchase #2	$65.38	4.108%	$68.0658	$68.07	$68.05	$68.10
Purchase #3	$52.31	3.850%	$54.3239	$54.32	$54.30	$54.30
Purchase #4	$98.39	13.704%	$111.8734	$111.87	$111.85	$111.90
Purchase #5	$6.85	10.209%	$7.5493	$7.55	$7.55	$7.50
Purchase #6	$176.63	13.517%	$200.5051	$200.51	$200.50	$200.50
Purchase #7	$196.75	6.378%	$209.2987	$209.30	$209.30	$209.30
7 purchase totals =	$710.25		$779.7850	$779.79	$779.70	$779.80